1. Field Of The Invention
The present invention related to a ferromagnetic metal-film-type recording medium and, more particularly, to a method of producing a magnetic recording medium of the type mentioned above, wherein durability of a protective layer and a top coating layer, which are formed after the formation of a magnetic layer to improve performance of practical use, is remarkably improved, as well as to an apparatus suitable for use in carrying out the method.
2. Description Of The Related Art
Ferromagnetic metal-film-type magnetic recording mediums have been known which are produced by forming, through vacuum evaporation, sputtering, ion plating or the like method conducted in a vacuum atmosphere, a film of Co, Ni, Fe or an alloy including one of those metals as the main components on a polymeric film such as a polyimide film or on a substrate which is made of a non-magnetic metal. These ferromagnetic metal-film-type magnetic recording mediums exhibit remarkably improved recording density as compared with conventional application-type magnetic recording medium.
In order to attain a high recording density, it is an important factor to diminish as much as possible any recording/reproduction defect, as well as to minimize spacing loss due to spacing between the magnetic recording medium and a magnetic head. Magnetic recording also is required to have high durability. In order to meet these requirements, hitherto, it has been known to cover a magnetic layer with a protective layer and, further, to form a lubrication layer as a top-coat layer.
FIG. 6 shows, in section, a known magnetic recording medium which has a protective film formed by a plasma CVD method (Chemical Vapor Deposition) and a lubrication layer formed by a wet-application method. Numeral 1 denotes a substrate, 2 denotes a ferromagnetic metal-film layer formed by vacuum film formation, 3 denotes a back coating layer, 4 denotes a protective layer formed by plasma CVD method, and 5 denotes a lubrication layer formed by wet-application method.
Examples of known method and apparatus for producing the known magnetic recording medium shown in FIG. 6 will be described with specific reference to FIGS. 6 and 7.
A description will be given first of a known apparatus for forming the protective layer 4 by a conventional plasma CVD method will be explained with specific reference to FIG. 7. A magnetic recording medium in the state before the formation of the protective layer 4, denoted by 10a, is wound on a supply roller 11. Numerals 12 and 14 denote pas rollers which rotate in contact with the ferromagnetic film layer 2 on the magnetic recording medium 10. Numeral 13 denotes a main roller which is insulated from the main part of the apparatus and which is capable of feeding the magnetic recording medium 10 in close contact with the ferromagnetic metallic film layer 2 with a predetermined voltage applied therebetween. Numeral 15 designates a take-up roller which continuously takes up the magnetic recording medium 10b after formation of the protective layer 4. Numeral 16 denotes a plasma generating nozzle, 17 denotes an electrode, 18 denotes a gas-introduction port, and 19 denotes a power supply for generating a plasma. These components 16 to 19 in cooperation provide a processing unit for forming the protective layer. Numeral 40 denotes a biasing power supply which applies a voltage between the main roller 13 and the ferromagnetic metal film layer 2 of the magnetic recording medium 10. The bias power supply 40 is disposed outside the vacuum container together with the plasma power supply 19.
A description will now be given of the method for producing the magnetic recording medium employing a known plasma CVD method.
The magnetic recording medium 10a in the state before the formation of the protective layer 4 is unwound from the supply roller 11 and is advanced through the pass roller 12. The magnetic recording medium 10a is further fed in close contact with the main roller 13 with a voltage applied between itself and the main roller 13. On the other hand, a plasma ion current for forming a protective layer is generated as a result of supply of a reaction gas from the gas introduction port 18 and the plasma power supply 19. The ion current is applied through the plasma nozzle 16 so as to reach the ferromagnetic metallic film layer 2 on the magnetic recording medium 10a thereby forming a protective layer 4. The magnetic recording medium 10b with the protective layer 4 formed thereon is taken up by the take-up roller 15 through the pass roller 14. The magnetic recording medium carrying the protective layer 4 formed thereby the above method is temporarily demounted from the plasma CVD apparatus, for the purpose of forming a lubrication layer thereon.
The magnetic recording medium produced by the above-described known method, however, exhibits a small bonding force between the protective layer 4 and the lubrication layer 5, so that the lubrication layer 5 tends to be scraped off by, for example, the magnetic head of a video tape recorder during reproduction. In consequence, since the lubrication layer 5 does not serve as lubricant, fluctuation in the reproduction output is caused due to insufficient lubrication causing troubles such as clogging in the head. Thus, the magnetic recording medium produced by the conventional method has a significant defect.